Soap compositions, for example, bars and liquids, are known to have antibacterial benefits largely associated with the removal of organisms from the skin through the cleansing/detergency action of such products. Additionally, such compositions commonly have biocidal action against many Gram negative bacteria. The biocidal action of soap compositions against Gram positive bacteria, such as for example S. aureus is, however, considerably more limited within the contact times typical of product use, generally under 1 minute, and more commonly on the order of 30 seconds or less. Achieving biocidal action against Gram positive bacteria is especially problematic in the case of high pH soap bars, by which is meant that a 1 wt. % solution thereof in water has a pH in a range of from 9 to 11 at 25° C.
Various routes to improving the biocidal activity of soap compositions have been suggested. For example, U.S. Pat. No. 6,794,344 (Taylor et al.) discloses soap bars that comprise at least about 50% soap having alkyl chain lengths of 8-10 carbon atoms, about 10% to about 30% hydric solvent, and free acid, preferably free fatty acid, such that the pH of a 10% aqueous solution of the soap bar is no greater than about 9. The soap bar is therein characterized as exhibiting, in the test therein described, a log reduction against Gram positive bacteria of at least 3 after 30 seconds of contact at 40° C., as measured against S. aureus. Information presented in Table 3 of Taylor et al. compares the effect of free fatty acid content as function of pH on antibacterial activity against S. aureus. 
Routes to achieving an antimicrobial benefit in cleansing compositions, including soap-based compositions, as well as compositions based on synthetic anionic surfactant, i.e., “syndet”, also include the use of one or more agents having a biocidal effect.
U.S. Patent Application Publication No. 2012/003413 (Levison et al.) discloses antiseptic formulations therein said to be capable of providing antimicrobial properties over an extended period of time. The formulations therein disclosed include chelated metal ions (including chelated silver ions) and a fixative polymer having the capacity to bond the chelated metal ions to the skin. In Table IV thereof, Levinson et al. provides the formulation for a liquid soap based on synthetic anionic surfactant. The formulation includes, among other ingredients, sodium laureth sulfate, sodium lauryl sulphate, propylene glycol, cocamidopropyl betaine, cocamide DEA, ethyol alcohol, macadamia glycerides, acrylate cross polymer, silver dihydrogen citrate, and tetrasodium EDTA.
WO 01/1131422 discloses toilet soap therein characterized as having antimicrobic properties, which soap contains what is therein termed a “soap basis”, functional additives, and bentonite powder intercalated with Ag+ and/or Cu2+ ions.
U.S. Patent Application. Publication No. 2010/0098776 (Carnali et al.) discloses soap-based liquid wash formulations therein said to have enhanced antibacterial activity, which compositions include from 0.01 to 10 wt. % antimicrobial agent, e.g., silver particles, zinc particles, copper particles or mixtures thereof. The soap-based formulations are said to include 10 to 50% by weight, preferably 25 to 40% by weight, more preferably 30 to 40% by weight of a fatty acid blend of C12-C18 fatty acids (the fatty acid blend being further characterized as having degrees of neutralization between 70% and 90%); 10 to 40% by weight of co-solvent such as, for example glycerol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and mixtures thereof, and less than 18%, preferably less than 16% by weight water, such that the ratio of co-solvent to water lies in the range of 0.4-10, preferably 0.8 to 7, more preferably 1.0 to 5.
U.S. Pat. No. 3,050,467 (Horowitz et al.) discloses antiseptic cleaners (for example, soaps and detergents) that include a mixture of from about 90% to about 99% by weight of a water-soluble soap and from about 10% to about 1% by weight of a silver salt of partially depolymerized alginic acid. The recited amount of alginic acid is said to provide the compositions with a silver content of from 0.01 to 1% by weight.
U.S. Patent Application Publication No. 2006/0115440 (Arata et al.) discloses personal care products that include silver dihydrogen citrate and a physiologically acceptable medium. The compositions are said to include silver ion at a concentration of 50 ppb to 10,000 ppm, such concentrations being based on the total weight of silver ion per unit volume of the final composition (if liquid) or per unit weight of the final composition (if solid).
There remains a need for soap bars, in particular high pH soap bars that provide improved biocidal activity against Gram positive and Gram negative bacteria in the relatively short contact times typical of bar use.